Automatic gauge and tension control system



INVENTOR. HARRY EUGENE BRYS,

ATTORNEYS AUTOMATIC GAUGE AND TENSION CONTROL SYSTEM Oct. 19, 1965 United States Patent 3,212,319 AUTOMATl-C GAUGE AND TENSION CONTROL SYSTEM Harry Eugene Brys, Butler, Pa, assignor to Arznco Steel Corporation, Middletown, Shin, a corporation of (Bhio Filed May 31, 1962, Ser. No. 199,082 11 Claims. (Cl. 72-12) This invention relates to an automatic gauge and tension control system for a tandem train of rolling mills such as are used in the cold rolling of steel strip. It is conventional to feed strip from a coil through a series of stands of rolling mills to a coiler and to adjust the speeds and screw-downs of the various mill stands in such manner that tension is maintained in the strip between the stands and also between the decoiler and the entrance stand and between the exit stand and the coiler. In this Way the working rolls can produce a greater reduction in gauge and each of the mill stands produces a portion of the total reduction in strip between the decoiler and coiler.

It is very desirable to maintain the gauge of the strip constant, or almost so, not only as it issues from the exit stand, but also between the various stands. It is also desirable to control the tension between the various stands so that the work is evenly divided among the several stands in the train.

Various methods have been attempted to accomplish the desired results but none has been completely over-all effective in preventing over-control or what is known as hunting.

One system which has been used in an elfort to maintain gauge and tension as constant a possible has been the so-called IR control system. Most mills are now conventionally provided with such IR control systems. In such systems the mill motor is usually energized by a generator, having a field powered by suitable excitation, and as the load on the working rolls of the mill changes, there is a change in the IR drop in the motor generator circuit. This change in the IR drop is applied to a supplementary field coil so that the generator field coil has the supplementary field coil added to it or subtracted from it to compensate for the change in load on the working rolls. Thus, if the load on the working rolls suddenly increases, the change in IR drop produces an increased field strength on the generator which powers the mill motor and thereby produces an increase in speed of the mill motor.

It is an object of the present invention to utilize the IR control system which is conventional in combination with other controls to achieve a better regulation of the speed of multi-stand mills and to maintain extremely uniform tension between the stands.

It is another object of the present invention to utilize means for measuring the tension between stands to produce a change in speed of a mill motor, either alone or in combination with the so-called IR control system.

It is another object to provide an automatic tension control system which employs a double-ended or null balance signal to effect control of this speed regulating device.

It is yet another object of the invention to use the automatic tension control in combination with a conventional 3,Zl2,3id Patented Get. 19, 1955 Ice IR control system together with an automatic screw-down control employing the signal impulse integrator with variable time delay as disclosed and claimed in my copending application, Serial No. 743,187, filed June 19, 1958, now US. Patent No. 3,109,966.

These and other objects of the invention which will be pointed out in more detail hereinafter, or which will become apparent to one skilled in the art as the description proceeds, are accomplished by that certain construction and arrangement of parts of which the following is a description of an exemplary embodiment.

Reference is made to the single figure of the drawing which somewhat diagrammatically shows a four stand tandem mill and which shows somewhat diagrmmatically the control systems in their relation thereto.

Briefly, in the practice of the invention I provide a device for measuring gauge of the strip such, for example, as a radiation or X-ray gauge such as are well known in the art and I preferably apply one such gauge immediately following the entrance mill stand and another immediately following the exit stand. The signals from these gauges are then caused to actuate the screw-down of the respective mill and preferably the screw-down is actuated through the signal impulses integrator with variable time delay mentioned above.

One mill stand which should be located near the middle of the train (in a train having an odd number of stands, it would be preferably the central stand and in a train having an even number of stands it would be one of the two stands adjacent the center of the train), is designated as the pivot stand and, although this stand will be provided with the conventional screw-down, no automatic means are provided to vary this screw-down during the operation of rolling strip. The pivot stand will preferably be provided with the conventional IR control system.

The mill or rn-ills ahead of the pivot mill will be provided with tensiometer control systems to be described in more detail hereinafter, and the exit stand will be provided with a combination of an IR control system and a tensiometer control.

Referring now in more detail to the drawing, there is shown by way of example a train of four mill stands which have been labeled Stands 1 through 4. The strip 6 is to be thought of as moving from right to left in the drawing and as being paid off a decoiler 5 and passing successively through the work rolls 27, 28 of stand 1, the work rolls 42, 43 of stand 2, the work rolls 66, 67 of stand 3, and the work rolls 57, 58 of stand 4 to a coiling device indicated at 7. It will be understood that the respective work rolls are backed up as is conventional by back up rolls of large diameter. The work rolls 27, 28 are driven by a mill motor 25. Similarly, the work rolls 42, 43 are driven by a motor 49, the rolls 66, 67 are driven by a motor 60 and the rolls 57, 58 are driven by a motor 55. Each of these mill motors is powered by a generator, the generators being respectively indicated at 24, 39, 59 and 54. The generators each have a field coil and the field coils are designated respectively at 23, 38, 64 and 53. It will be understood that the several field coils are energized by a suitable source of power, either rotating or static, such as the field control devices 21, 36, 51 and 62. The respective motor generator combinations are connected together in conventional manner and are 3 provided with resistance as indicated respectively at 26, 41, 61 and 56.

In connection with stand 3, there has been shown the conventional IR control system. It will be observed that a supplementary field coil 63 has been shown for the generator 59 and that the coil 63 is connected up so that the IR drop across resistance 61 in the motor generator circuit will be impressed thereon. It will be understood that as this IR drop changes, the total effect of the field control device 62 comprising the coils 63 and 64 will be changed and change in the total effect of the field 62 will cause the speed of the motor 60 to increase or decrease. This IR control system as used on stand No. 3 is conventional and according to the present invention it is used alone only on the pivot mill which in the four stand train shown is stand No. 3.

Between stands No. 1 and 2, there is shown a thickness gauge 8 which may be, as pointed out above, of any suitable type but is preferably a radiation or X-ray gauge. The broken lines indicate that a signal from the gauge 8 may be applied to stand 1 or stand 2 through the devices indicated at 9 and 10 respectively. These devices 9 and 10 will not be described here in detail and reference is made for an understanding of their operation to said copending application Serial No. 743,187, now Patent No. 3,109,966. Suffice it to say that the devices 9 and 10 will not pass a signal if it is below a predetermined magnitude. It will also integrate a series of signals and accumulate successive short duration signal impulses so that smoother and more realistic corrections are made on the screw-down mechanism. The greater the magnitude of the error signal, the shorter will be the time delay involved and consequently the faster the response. Successive signals of opposite sign will tend to cancel each other and the overall effect of the devices 9 and 10 is to prevent over-control and hunting which would result from short duration impulses above the threshold value, and also it has the effect of integrating successive impulses which, although not directly effecting the controller, nevertheless will effect the duration of the time delay.

In any event, by the device described in the said copending application, the suitably integrated and time delayed signal from the gauge 8 is caused to appropriately actuate the screw-down of stand No. 1 or optionally the screws of stand No.2.

Similarly, the gauge 11 which is similar to the gauge 8 operates through the signal impulse integrator with variable time delay indicated by the box 12, to actuate the screw-down of stand No. 4.

As to the two mills on the entrance side of the pivot stand, i.e. stands 1 and 2, there are indicated the tensiometers 13 and 29. The tensiometer 13 is arranged to measure the tension on the strip between stands 1 and 2 and the tensiometer 29 is arranged to measure the tension between stand No. 2 and the pivot stand No. 3.

At 14 and 30 there are indicated differential detector amplifier devices. Such devices function to compare two signal inputs and amplify the difference between the two signals to produce an output of reversible polarity. Thus, as to the differential detector amplifier 14, the input from the tensiometer 13 is shown at 15, while 17 is an input signal put in by the operator by means of a manual control 16. The device 14 compares the signal 15 against the reference signal 17 and amplifies this difference at the output 18. The output 18 is therefore a signal based upon the difference in the strip tension between stands 1 and 2 from a predetermined desired value set in by the operator at 16. The output signal from 18 is impressed upon a coil 22 constituting a part of the field control device 21 of the generator 24. The signal at 18 will have a polarity depending upon whether the signal 15 is greater or less than the signal 17. The signal at 22 is thus algebraically added to the field 23 and thus the speed of the mill motor 25 is controlled in accordance with changes in tension from the predetermined standard as measured by the tensiometer 139. It will be seen that this system is really a double-ended or null balance signal. When the tension as read by the tensiometer 13 is at the desired value, the mill speed is unaffected. If, for example, the desired tension of ten thousand pounds drops to seven thousand pounds, the device 14 signals the speed change to the mill motor 25 in magnitude proportional to the er; ror. As the mill speed begins to correct the tension, the tensiometer is returning toward the null point and the corrective signal is decreasing so that the mill motor is brought to correct speed more gradually without overshooting. Theoretically, the tension will never reach null balance from the corrective signal alone but it is held very close to the desired value and, since normal tension variation due to gauge or screw changes are of short duration, the tension is regulated very accurately from start to finish of coils.

The tension control for mill stand No. 2 may be the same as that just described, with the tensiometer 29 corresponding to the tensiometer 13, the inputs 31 and 33 corresponding respectively to the inputs 15 and 17, the manual control 32 corresponding to the manual control 16, the output 34- corresponding to the output 18 and the field coil 37 corresponding to the field coil 22.

From the foregoing, it will be seen that the speeds of the mill motors for stands 1 and 2 may be varied on the basis of tensiometer control only and that the speed of the mill motor of the pivot stand No. 3 may be varied by means of IR control only.

Corning now to stand No. 4, this stand is provided with a mil motor 55 powered by a generator 54. The field coil 53 corresponds to the field coils 23, 38, and 64. This mill motor 55 is provided with a speed control based on IR drop with the coil 65 corresponding to the coil 63 in connection with the mill motor 60 on stand 3. Additionally, the speed of mill motor 55 is provided with a tensiometer control as above described wherein the tensiometer 44 corresponds to tensiometers 13 and 29, the input 46 corresponds to the inputs 15 and 31, the input 48 corresponds to the inputs 17 and 33, with the manual control for the input 48 being shown at 47. The output 49 corresponds to the outputs 18 and 34 and the field coil 52 corresponds to the coils 22 and 37. The only difierence is that, whereas the tensiometers 13 and 29 operate to control the speed of the mill motor of the mill stand ahead of the tensiometer, the tensiometer 44 is arranged to exert control on the mill motor of the stand following the tensiometer.

It will now be clear that while stands 1 and 2 (or any stands ahead of the pivot stands) have their motors controlled on the basis of tensiometer control only and the pivot stand has its motor controlled by IR control only, the exit stand 4 has its mill motor speed controlled by a combination of tensiometer control and IR control.

The mill master rheostat is indicated at 20, and is mechanically coupled to the individual rheostats for the individual stands at 19, and 50. The sliders of the rheostats 19, 35 and are provided with an open section so that, when the mill is at threading speeds, the automatic tension control is removed. As the mill motors are brought up to operating speeds by the master rheostat 20 through conventional circuity (not shown), the individual rheostats serve to allow a proportionate amount of current to flow to the field control devices of the separate stands, thus providing the required sensitivity for any given mill speed.

As stated previously, any suitable type of field control device may be used at 21, 36, 62 and 51, and the generator may be replaced by other suitable devices without departing from the spirit of the invention.

From the foregoing description, it will now be understood that a novel feature is the control of thicknes or gauge by varying the tension by means of IR control in conjunction with tensiometer tension control. The amount of correction obtainable has been heretofore limited, due to the fact that a mill motor may be forced into run-away condition on IR compensation alone.

Furthermore, prior applications of IR compensation control have taken the no-load speed and the full-load speed and fed in enough IR compensation so that the speed at full-load is approximately equal to, but somewhat less than, the speed at no-load, e.g. about 75% of no-load speed. In the present invention enough compensation is provided so that the full-load speed is greater than the no-load speed, e.g. about 110% of the no-load speed. This is made possible by feeding into the motor speed control a signal from the tension measuring system, which serves to limit the mill motor speed, and to provide additional mill motor speed control. Optimum results are achieved by the use of a double-ended signal or null system, wherein the control operates in both directions from a balanced condition. In the present invention, the IR change occurring inthe mill motor due to gauge change creates an inmmediate change in tension between stands, which change in tension is of sufficient magnitude to control effectively the variation in gauge before it reaches the thickness measuring gauge. The factors which make this possible are that the current or load change on the mill motor must result from a thickness change rather than inter-stand changes. This is made possible by a closely controlled tension. Secondly, the mill motor should be what is known as stiff, that is it has speed compensation built into it. Although this is desirable, it is not absolutely necessary since droop correction may be provided by other means. Third, the automatic tension control system must have a small time delay to allow the IR control to effect an immediate change for gauge variations of small magnitude and short duration. Fourth, the automatic screw-down control cooperates eifectively where the necessary compensation is greater in magnitude than can be compensated by IR control, in that, if the screws are jogged downward, for example, pressure is applied producing a load increase on the mill and the mill motor. The normal effect on tension between the stands being controlled is a decrease of tension. The IR control sensing the added load on the mill caused by the screw-down correction will increase the speed (in the case of No. 4 stand), thereby effectively increasing or maintaining the tension, and also thereby increasing the effectiveness of the screw-down action.

It will be understood that numerous modifications may be made without departing from the spirit of the invention and I therefore do not intend to limit myself otherwise than as set forth in the claims which follow.

Having now fully described my invention, what is claimed as new and is desired to secure by Letters Patent is:

1. In a tandem train of cold rolling mills comprising at least an entrance mill stand, an exit mill stand, and a pivot mill stand therebetween, automatic screw-down control means for said entrance and exit stands, means for supplying electrical energy to the mill motor of each stand, mill motor speed control means for said pivot stand, means for predetermining a desired strip tension between said entrance stand and the succeeding stand, means for measuring strip tension between said entrance stand and succeeding stand, and mill motor speed control means for said entrance stand actuated in response to changes in tension with respect to said predetermined tension, means for predetermining a desired strip tension between said exit stand and the preceding stand, means for measuring strip tension between said exit stand and preceding stand, and mill motor speed control means for said exit stand actuated in response to changes in tension with respect to the predetermined tension ahead of said exit stand, said exit stand having also mill motor speed control means actuated in response to changes in load on said exit stand, whereby the speed of the mill motor of the entrance stand is controlled in response to changes in tension between it and the succeeding stand only, the speed of the mill motor of the pivot stand being controlled as a reference, and the speed of the mill motor of said exit stand is controlled in response to a combination of the changes in tension between it and the preceding stand and the changes in load on said exit stand.

2. Apparatus according to claim 1, said train comprising four mill stands, the pivot stand being the stand immediately preceding the exit stand, the stand between the pivot stand and the entrance stand, being the No. 2 stand, having also automatic screw-down control means, means for predetermining a desired strip tension between said No. 2 stand and said pivot stand, and mill motor speed control means actuated in response to changes in tension with respect to the predetermined tension between said No. 2 stand and said pivot stand, the speed of the mill motor of said No. 2 stand thus being controlled in response to changes in tension between it and said pivot stand only.

3. Apparatus according to claim 1, said train comprising four mill stands, the pivot stand being the stand immediately following the entrance stand, the stand between the pivot stand and the exit stand being the No. 3 stand, and having the speed of its mill motor controlled in response to changes in tension between it and said pivot stand only.

4. Apparatus according to claim 1, wherein said train comprises five mill stands, the middle one of said stands being the pivot stand.

5. Apparatus according to claim 1, wherein each of the means for predetermining a desired strip tension and actuating a mill motor speed control in response to variations from said predetermined tension comprises a tensiometer, and a difierential detector amplifier device, means for feeding into said device an arbitrary signal corresponding to said predetermined tension, means for feeding into said device a signal corresponding to the actually existing tension as determined by said tensiometer, and means to cause the output of said device, corresponding to the plus or minus variation of actual tension from said predtermined tension, to affect the speed of said mill motor.

6. Apparatus according to claim 5, wherein the output signal from said device is algebraically added to the electrical energy supplied to said mill motor.

7. In a tandem train of cold rolling mills comprising at least three mill stands, one of said stands, as nearly in the middle of said train as possible, constituting the pivot stands a tensiometer on the exit side of each of said stands ahead; of said pivot stand, and on the entrance side of the exit stand, difierential detecting and amplifying means for each tensiometer, means for feeding the signal from each tensiometer into the respective detecting and amplifying means, means for feeding into said detecting and amplifying means an arbitrary signal, said detecting and amplifying means having an output signal proportional to a difference between said two fed-in signals, said output signal being of one polarity if the tensiometer signal is greater than said arbitrary signal, and of the other polarity if the tensiometer signal is smaller than said arbitrary signal, means for causing said output signal from the detecting and amplifying means ahead of said pivot stand to vary the speed of the mill motor ahead of the respective tensiometer, each of said mill stands after said pivot stand having means to control the mill motor thereof to compensate for IR changes resulting from changes in the load of the respective stands, and means for causing the output signal from each of the detecting and amplifying means after said pivot stand to be superimposed upon the IR control means of the mill stands after the respective tensiometer.

8. Apparatus according to claim 7, said train comprising four mill stands, the pivot stand being the stand immediately preceding the exit stand, and there being a stand between said entrance stand and said pivot stand.

9. Apparatus according to claim 7, said train comprising four mill stands, the pivot stand being the stand immediately following the entrance stand, and there being a stand between said pivot stand and said exit stand.

10. Apparatus according to claim 7, wherein said train comprises five mill stands, the middle one of said stands being the pivot stand.

11. Apparatus according to claim 7, wherein each of 1 0 0 References Cited by the'Examiner UNITED STATES PATENTS 1,988,930 1/35 Winne 80-351 2,342,767 2/44 Stoltz 8035.1 2,949,799 8/60 Walker 8035.1 3,024,404 3/62 Zitfer 8056.2

OTHER REFERENCES Control Engineering, pages 116, 117, September 1956.

WILLIAM J. STEPHENSON, Primary Examiner.

CHARLES W. LANHAM, Examiner. 

1. IN A TANDEM TRAIN OF COLD ROLLING MILLS COMPRISING AT LEAST AN ENTRANCE MILL STAND, AN EXIT MILL STAND, AND A PIVOT MILL STAND THEREBETWEEN, AUTOMATIC SCREW-DOWN CONTROL MEANS FOR SAID ENTRANCE AND EXIT STANDS, MEANS FRO SUPPLYING ELECTRICAL ENERGY TO THE MILL MOTOR OF EACH STAND, MILL MOTRO SPEED CONTROL MEANS FOR SAID PIVOT STAND, MEAND FOR PREDETERMINING A DESIRED STRIP TENSION BETWEEN SAID ENTRANCE STAND AND THE SUCCEEDING STAND, MEANS FOR MEASURING STRIP TENSION BETWEEN SAID ENTRANCE MEAND FOR MEASURING STRIP TENSION BETWEEN SAID ENTRANCE MEANS FOR SAID ENTRANCE STAND ACTUATED IN RESPONSE TO CHANGES IN TENSION WITH RESPECT TO SAID PREDETERMINED TENSION, MEANS FOR PREDETERMINING A DESIRED STRIP TENSION BETWEEN SAID EXIT STAND AND THE PRECEDING STAND, MEANS FOR MEASURING STRIP TENSION BETWEEN SAID EXIT STAND AND PROCEEDING STAND, AND MILL MOTOR SPEED CONTROL MEANS FOR SAID EXIT STAND ACTUATED IN RESPONSE TO CHANGES IN TENSION WITH RESPECT TO THE PREDETERMINED TENSION AHEAD OF SAID EXIT STAND, SAID EXIT STAND HAVING ALSO MILL MOTOR SPEED CONTROL MEANS ACUTATED IN RESPONSE TO CHANGES IN LOAD ON SAID EXIT STAND, WHEREBY THE SPEED OF THE MILL MOTOR OF THE ENGTANCE STAND IS CONTROLLED IN RESPONSE TO CHANGES IN TENSION BETWEEN IT AND THE SUCCEEDING STAND ONLY, THE SPEED OF THE MILL MOTRO OF THE PIVOT STAND BEING CONTROLLED AS A REFERENCE, AND THE SPEED OF THE MILL MOTOR OF SAID EXIT STAND IS CONTROLLED IN RESPONSE TO A COMBINATION OF THE CHANGES IN TENSION BETWEEN IT AND THE PRECEDING STAND AND THE CHANGES IN LOAD ON SAID EXIT STAND. 